A Global Positioning System (GPS) receiver typically includes an antenna, an RF front end unit, a filtering unit, amplifying circuits, a carrier recovery unit, a correlation unit, and a calculating unit that performs range calculations.
It is known that a GPS receiver can be heavily disturbed for several reasons if interfered by an RF signal, such as a Global System for Mobile Communications (GSM) signal. The RF front end will be saturated, the GSM signal will go through the filters and corrupt the correlation and the GSM broadband phase noise will increase the noise floor in the receiver.
In units including both a GPS receiver and a GSM transmitter it is known to use a signal from the GSM transmitter to determine if the GSM transmitter is active. This is then used to disable the Automatic Gain Control (AGC) of the amplifying circuits in the GPS receiver during the GSM burst.
It is also known to provide a filtering unit in the GPS system with isolation that has been optimized for GSM signals.